The rear ac blows very hot and cooks my kids in the back seat. Would a bad mono valve cause the rear to malfunction while allowing the front compartments ac to work fine???

 

I had similar problem occur with my 1993 600. There is a separate dual valve (sometimes mistakenly called a mono valve) for the front and the rear a/c controls. alldata.com or repair manuals show their locations. Each valve unit controls either the front or the rear coolant flow. I used the on-board a/c diagnostics to verify the valve was bad and not the temp control wheels assembly. My rear a/c dual valve was located behind an outside body panel just behind front right wheel. You can buy the dual valve at several online parts places. Shop around in Google, etc, by searching for Mercedes "duo valve" or "mono valve", as they cost a few hundred dollars each. Front duo valve has about six hoses attached. Rear duo valve four hoses. Both a bit difficult to get to, but doable. Cost me almost $600 to replace both duo valves (front and rear), as they do wear out (they work hard all the time), and I never wanted to have the problem again. Run the diagnostics first to verify. Bill M.

 

Thanks Bill, I really appreciate the help!!

Ron